Hormones That Regulate Calcium & Phosphate Homeostasis

Homeostasis is the activity performed by many life forms to maintain stable internal conditions throughout the organism. The human body uses calcium and phosphate in several ways, notably to build bones. Calcium is also an important factor for neuron communication, blood clotting and muscle contraction. Phosphates are used during energy metabolism, are part of the structure of cell membranes, and are an essential structural component of DNA and RNA. Hormones can influence the body's levels of calcium and phosphate, and play a critical role in their regulation.

Hormones are regulatory substances. There are different types classified generally as peptide (or protein) hormones, lipid hormones, and monoamines, which are modified single amino acids. Special cells and tissues (glands) are responsible for producing hormones. Hormones are secreted directly into the bloodstream or into the spaces between cells. Hormones may increase or decrease the concentration of certain substances within the body. Various biochemical signaling mechanisms stimulate or dampen hormone production. Problems with hormonal production can lead to serious diseases and even death. In some cases, your actions can affect hormone production. For example, when you consume sugary foods, your body releases the hormone insulin in reaction to high levels of sugar in the bloodstream.

The hormones calcitriol, calcitonin and parathyroid regulate body calcium. Specialized cells in the kidneys produce the hormone calcitriol, a form of vitamin D, when calcium levels in the blood are too low. This hormone increases the body's uptake of calcium from food and the release of calcium from the bones. Parathyroid hormone, or PTH, is secreted by the parathyroid glands and increases blood levels of calcium by stimulating bones to release calcium, stimulating kidney cells to reclaim calcium from urine before excretion, and increasing calcium absorption by the intestine. The hormone calcitonin, on the other hand, lowers calcium levels in the blood. Its production is stimulated by calcium levels in the blood that are too high. It is produced by the C-cells of the thyroid gland and works by suppressing calcium release from bones, dampening calcium absorption in the intestine and discouraging the kidneys from reabsorbing calcium from urine.

PTH and calcitriol also regulate phosphate in the body. PTH helps lower blood phosphate levels. It does this by reducing the reabsorption of phosphates dissolved in urine in the kidneys, causing more excretion of phosphates. Calcitriol raises the level of phosphate in the blood by promoting its absorption by the intestine. Calcitriol's effect on both phosphate and calcium, therefore, is to increase levels. This works well with calcitriol's role in promoting bone deposition, which requires both calcium and phosphate.

Many things can cause disruptions in homeostasis, and numerous problems can arise from those disruptions. Vitamin D deficiency, thyroid tumors, underactive or surgically removed parathyroids, or pregnancy and lactation can all result in a condition called hypocalcemia, or blood calcium deficiency. Symptoms of low blood calcium include excessive nervous excitability, muscle tremors and spasms, and even tetany. Hypercalcemia, or too much blood calcium, is relatively rare, but lethargy and muscle weakness are among possible symptoms. Disrupted phosphate regulation can also, rarely, become clinically significant. Vitamin D, calcium or phosphate deficiency can cause weak bones or rickets.